1. Field of the Invention
This invention relates to means for reducing paraffin deposits in the production tubing of oil wells, and more particularly to a hot oil plug supported on a tubing string collar within a casing to restrict the flow of hot oil pumped into the casing-tubing annulus to provide sufficient contact time for maximum heat transfer between the hot oil and the tubing, rods, and fluid inside the tubing, causing the paraffin to melt and be produced along with the well fluids.
2. Brief Description of the Prior Art
Restricted production is a common problem in oil wells producing oil with a high level of paraffin content. Paraffin wax collects on the tubing and flowline walls and on the body of the sucker rods (in the case of pumping wells). The paraffin buildup may eventually cause blockage, and measures must be taken to remove it.
Common methods for removing the paraffin deposits include scraping the interior of the production tubing, or closing down the well and washing with a suitable paraffin solvent. The result in either event is costly in a direct material way as well as in the loss of production.
The method of paraffin removal most often used on pumping wells is "hot oiling," which involves pumping hot oil, at about 160.degree. to 280.degree. F. down the annular space between the tubing and the casing. The hot oil heats the tubing, rods, and fluid inside the tubing, to melt the paraffin for production along with the well fluids.
The major problem with the "hot oil" treatment is that most pumping wells have very low producing bottom hole pressures. As a result, the hot oil falls down the annulus so fast that there is insufficient contact time for efficient heat transfer, and the effectiveness of the treatment is reduced.
Prior art methods include complex apparatus directed toward removing debris from well bores and for chemically treating wells which must be installed in the well bore or on the tubing string. There are sevreal patents on apparatus and methods directed toward restricting paraffin formation in wells.
Tuggle et al, U.S. Pat. No. 3,454,464 discloses a method for restricting paraffin deposits in flowing oil wells by effecting a sharp drop in pressure sufficient to refrigerate the flow by vaporization and expansion of normally gaseous fractions and precipitate the wax as suspended particles which flow away with the produced oil.
Hewes, U.S. Pat. No. 4,049,057 discloses a valve unit which is placed in the eduction tube of an oil well used for removal of paraffin. The unit contains one ball valve to discharge fluid from the eduction tube into the annulus between the tube and the casing, and another ball valve to receive fluid from the annulus into the eduction tube.
McCulloch, U.S. Pat. No. 2,798,558 discloses a well completion apparatus comprising a packing member which isolates the annulus between the casing and tubing. An elongated conduit containing a valve extends through the packing member to allow communication between the annular with the casing below the tower open end of the tubing. The invention is directed to apparatus for conducting operations in a well casing without manipulating tubing therein.
Neither the prior art in general nor these patents in particular disclose the present invention of a hot oil plug which is slidably received on the production tubing string and supported on one of the tubing string collars within a casing, the outside diameter of the plug being smaller in diameter than the drift diameter of the casing to provide an annular space therebetween. The hot oil plug restricts the rate of flow of hot oil pumped into the casing-tubing annulus by allowing the oil to pass slowly through the annular space between the plug and the casing and through a series of circumferentially spaced apertures resulting in a reduced flow rate providing sufficient contact time to produce maximum heat transfer between the hot oil and the tubing, rods, and fluid inside the tubing, causing the paraffin to melt and be produced along with the well fluids.
The apertures allow passage of pressurized gases from the annulus below the hot oil plug to the annulus above the hot oil plug to prevent gas locking and reduced production through the production tubing. The plug may also be provided with a series of circumferentially spaced check valves in place of, or in combination with the apertures to allow passage of the pressurized gases.